This invention refers to a circuit arrangement for a reversible electric motor supplied from a voltage source, which motor drives a combined window-lifter and door locking installation in motor vehicles and may be switched on via a first operating switch developed as a reversing switch and via a second operating switch serving as a central switch to which a position switch is assigned which is developed as a two-way switch.
Several versions of such a circuit arrangement are known from the German laid open print 2,854,670. In these embodiments the position switch, at the end of the locking operation, is moved from a first switching position to a second switching position and, at the end of the unlocking operation, from the second switching position back to the first switching position. If, like in one of the embodiments, a further switch were not provided so, if one wished to close a window via the reversing switch, it could only be completely closed in most instances in connection with a locking of the door. Such an embodiment involves the disadvantage that the vehicle can be locked en route which is not desired on grounds of safety. In order not to lock the door, when the window is completely closed, in another version a normally closed switch is inserted between the terminal of the electric motor which is connected to the position switch and a make contact of the reversing switch which is closed, when the window pane is moved and which is opened as soon as the window has reached its closed position. The switch is opened, the circuit of the electric motor is interrupted upon termination of the closing process, so that it becomes more unlikely that the door will be locked. One cannot entirely exclude a locking, because the circuit of the motor is only interrupted, but the motor is not short-circuited.
Eventually by the German laid open print 2,854,670 a further circuit arrangement has been suggested in which the position switch is designed in such a way that it changes over for a short time, when it is actuated, thereby short-circuits the motor and after expiration of a delay time automatically returns to its rest position, in which the motor circuit is closed. When this position switch is actuated at the end of each unlocking of the door and of each closing of the window it is achieved with great reliability that the window is not opened, when the door is unlocked and that the door is not locked, when the window is closed. The design of a position switch which automatically returns to its rest position with a certain delay time after it was actuated is, however, very complicated.
It is the object of the present invention to develop a circuit arrangement including the features of the invention in such a way that the electric motor is controlled with a small amount of circuitry and simply developed switching means in such a way that it is short-circuited after closing of a window and after unlocking of the doors. Of course the mode of operation of the circuit arrangement is not to be disadvantageously affected.